Shelf



FIG. 1 is a front plan view of a shelf;

FIG. 2 is a side plan view thereof, which is a mirror image of the opposite side thereof;

FIG. 3 is a top plan view thereof; and,

FIG. 4 is a perspective view thereof; and,

FIG. 5 is a further perspective view. 

The ornamental design for a shelf, as shown and described. 